Systems in which information can be transmitted or received by the use of a wireless signal between a wireless tag which is attached to an article or a person and in which identification information is embedded and a reader-writer have been put to practical use in various fields. Wireless tags are also referred to as radio frequency identification (RFID) tags and include antennas and integrated circuit (IC) chips connected thereto.
In many cases, wireless tags are mass-produced by the use of resin materials or the like.
Japanese Laid-open Patent Publication No. 2009-224959
Japanese Laid-open Patent Publication No. 2005-30877
Japanese National Publication of International Patent Application No. 2009-507382
By the way, with such wireless tags the performance of protecting an antenna may be degraded because of moisture absorption by a resin material or ultraviolet rays. Furthermore, an antenna may be disconnected because of treatment by a user or a crack or the like may appear in a connection between an IC chip and an antenna portion.
In order to detect such degradation of a wireless tag, a measuring device used for measuring the intensity of a signal returned from a wireless tag may be prepared in addition to a reader-writer. By doing so, measurement is made in an environment in which the influence of electromagnetic waves is small. With a wireless tag which receives electric power by resonance, the degradation of an antenna causes a change in input impedance and a resonance frequency deviates from the original resonance frequency. Accordingly, a reader-writer whose resonance frequency is variable is prepared in order to compensate for it.
As stated above, to arrange an evaluation environment costs much labor. Accordingly, it is difficult to detect the degradation of a wireless tag.